Formation of Photoconductive and Photovoltaic Films

ABSTRACT

The present application discloses a method and system of depositing a lead selenide film onto another material. The lead selenide film may used in a photoconductive application or a photovoltaic application. Furthermore, the applications may be responsive to infrared radiation at ambient temperature. In one embodiment, a method includes sputtering the lead selenide film, performing a sensitization process, and applying a passivation film. In one exemplary embodiment, a p-n junction is formed by directly adhering a lead selenide film to a silicon substrate.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/266,372, filed Nov. 6, 2008, which is a continuation-in-part of U.S.patent application Ser. No. 11/059,981, filed Feb. 17, 2005 (now U.S.Pat. No. 8,061,299, issued Nov. 22, 2011). The '299 patent claimspriority to UES, Provisional Application No. 60/545,249, filed Feb. 17,2004, which is hereby incorporated by reference. Furthermore, thisapplication claims priority to U.S. Provisional Application No.60/985,876; filed Nov. 6, 2007 and to U.S. Provisional Application No.61/025,141, filed Jan. 31, 2008.

FIELD OF INVENTION

The present application relates to systems and methods for depositingmaterial regions onto substrates, More specifically, the presentapplication relates to systems and methods for depositing a leadselenide film onto various materials, such as a silicon substrate.

BACKGROUND OF THE INVENTION

The use of lead salt materials, such as lead sulfide (PM), lead selenide(PbSe), and lead telluride (PbTe), in photoconductive and photovoltaicapplications is well known in the art. Lead salt materials have band gapenergies which allow the absorption of radiation in the infraredspectrum. In photoconductive applications, the absorption of infraredradiation by the lead salt material provides a change in itsconductivity. The change in the conductivity can be sensed by sensing acurrent flowing therethrough. In this way, the lead salt material can beused to sense incident radiation. In photovoltaic applications, theabsorption of infrared radiation in the lead salt material provides apotential difference. The potential difference can be used to provideelectrical power. Accordingly, lead salt materials can be used inoptoelectronic devices such as infrared photodetectors, solar cells, andthermoelectric devices, among others.

Typically, lead salt materials are deposited on a substrate, such as asilicon substrate, by evaporation or chemical bath deposition. However,these deposition methods have several problems. One problem is that thedeposited lead salt material may not adhere to the substrate properly.This is particularly a problem if the substrate is silicon. If the leadsalt material does not adhere properly, then the yield of devices islow, which increases the costs.

Another problem is that it is difficult to control the composition ofthe deposited lead salt material. As a result, the composition of thelead salt material tends to be different from one deposition to another.This is further complicated because the composition can undesirablychange with time after it is deposited and exposed to the outsideatmosphere. The electrical and/or optical properties of the lead saltmaterial depends on the composition, so if the composition changes thenthese will too.

A further problem is that it is typically desired to sensitize the leadsalt material. After it is sensitized, the lead salt material issensitive to incident IR radiation at higher temperatures, such as roomtemperature, in comparison to the typical cold temperatures used.Sensitization is usually done by exposing the lead salt material tooxygen. The sensitization can be characterized by measuring theresistivity of the lead salt material. However, the sensitization oflead salt material regions using conventional methods often leads toundesirable differences in resistivity from one lead salt materialregion to another.

These problems limit the usefulness of any devices formed with lead saltmaterials fabricated using conventional deposition systems and methods.Hence, there is a need for better systems and methods for depositinglead salt material regions onto substrates.

SUMMARY OF THE INVENTION

The present application provides a deposition system which includes avacuum reaction chamber with a substrate holder positioned in it. Afirst sputtering apparatus and a first plasma enhanced chemical vapordeposition (PECVD) apparatus are also positioned in the vacuum reactionchamber. In one example, the substrate holder holds a substrate. Sincethe first sputtering apparatus is configured to direct sputteredmaterial towards the substrate holder, the sputtered material will bedeposited on the substrate to form a sputtered material region thereon.The first PECVD apparatus is configured to deposit a PECVD materialregion thereon the substrate or the sputtered material region. It shouldbe noted that a material region can include one or more layers of thesame or different materials. Further, each layer can include an alloy ofa material which includes two or more different elements in variouscompositions.

The first PECVD apparatus includes a first PECVD electrode movable froma first position towards the substrate holder and a second position awayfrom the substrate holder. In the first position, the first electrodecan provide a plasma near the substrate holder in response to apotential difference between the first electrode and substrate holder.The first PECVD apparatus can also include a gas line which provides atleast one of oxygen gas and halogen gas to sensitize the material regionthat has been sputtered onto the substrate with the first sputteringapparatus.

The deposition system can further include a second sputtering apparatuspositioned in the vacuum reaction chamber. The second sputteringapparatus is configured to direct sputtered material towards thesubstrate holder so that it is deposited on the substrate. In someembodiments, the first sputtering apparatus can include a first targetof a first lead salt material and the second sputtering apparatus caninclude a second target of a second lead salt material. Hence, lead saltmaterial regions which include two different lead salt materials can besputtered onto the substrate. The two different lead salt materials canbe sputtered sequentially to provide two separate lead salt regionspositioned on top of each other or they can be sputtered at the sametime to form a material region which includes a lead salt alloy.

The deposition system can also include a second PECVD apparatuspositioned in the vacuum reaction chamber. The second PECVD apparatus isconfigured to deposit a second PECVD material region thereon thesubstrate. The second PECVD apparatus includes a second PECVD electrodemovable from a first position towards the substrate holder and a secondposition away from the substrate holder.

The present application further provides a deposition system whichincludes a vacuum reaction chamber with a substrate holder positioned init. The substrate holder is configured to hold a substrate. A sputteringapparatus is also positioned in the reaction chamber. The sputteringapparatus includes a first target and a first electrode coupled to it.The first target can include lead salt material. A first gas lineprovides a sputtering gas into the reaction chamber. The first gas linecan be positioned to output the sputtering gas toward the first target,The sputtering gas impacts the first target to sputter portions of thefirst target onto the substrate in response to a potential differencebetween the first electrode and the

A plasma enhanced chemical vapor deposition (PECVD) apparatus is alsopositioned in the reaction chamber. The PECVD apparatus includes asecond electrode movable between a first position between the firsttarget and substrate and a second position away from the first targetand substrate. A plasma is formed between the second electrode and thesubstrate when the second electrode is in the first position. A secondgas line provides a process gas into the reaction chamber so that it canbe decomposed into reactant gases by the plasma. The second gas line canbe positioned to output the process gas toward the substrate so that itreacts with the substrate more efficiently.

The deposition system can include a second sputtering apparatus with asecond target positioned near the first target and a third electrodecoupled to the second target. The sputtering gas impacts the secondtarget sputtering portions of the second target onto the substrate inresponse to a potential difference between the third electrode andsubstrate. The first target can include a first lead salt material andthe second target can include a second lead salt material. The firstlead salt material can be the same or different from the second leadsalt material.

The deposition system can include a second PECVD apparatus with a fourthelectrode movable from a first position between the second target andsubstrate and a second position away from the second target andsubstrate. The first and second targets and the second and fourthelectrodes can be oriented at non-zero angles relative to the substrate.

The deposition system can include an iodine gas source coupled to thesecond gas line. The iodine gas source can include a container withsolid iodine positioned in it. A heater is positioned to heat the solidiodine forming an iodine gas. A temperature control system is to thecontainer to monitor the temperature of the iodine gas. A pressurecontrol system is also coupled to the container to monitor a pressure ofthe iodine gas inside the container. A container gas outlet ispositioned to allow an amount of the iodine gas in the container to flowto the second gas line. The temperature control system adjusts theamount of heat provided by the heater in response to a feedback signalprovided by the pressure control system. The feedback signal indicatesthe pressure of the iodine gas in the container. In this way, thetemperature and pressure of the iodine gas can be controlled so that theamount of iodine gas is flowed through the second gas line.

The present application further provides a deposition system with asubstrate transfer housing having a plurality of openings. A door iscoupled to each opening of the substrate transfer housing. Each door ismovable between a first position away from the substrate transferhousing and a second position enclosing the substrate transfer housing.A substrate holder chamber is coupled to at least one opening of thesubstrate transfer housing. At least one sputter deposition system andat least one plasma enhanced chemical vapor deposition (PECVD) systemare also coupled to at least one opening of the substrate transferhousing. In this way, a substrate can be transferred between the atleast one sputter deposition system and the at least one PECVD systemwithout undesirably exposing the substrate to the outside atmospherebetween depositions.

The present application also provides a method of depositing a lead saltmaterial region. The method includes providing a reaction chamber andpositioning a substrate and a lead salt sputtering target into it. Asputtering gas is provided into the reaction chamber and a pressure isprovided therein. The step of providing the sputtering gas can alsoinclude providing a reactant gas into the reaction chamber. The reactantgas can include at least one a sensitizing gas and a dopant gas. Aportion of a first lead salt sputtering target is sputtered onto thesubstrate to form a first sputtered material region. In someembodiments, the method can include a step of depositing a seal coatingmaterial region on the first sputtered material region.

The method can include an optional step of sputtering a portion of asecond lead salt sputtering target onto the first lead salt materialregion to form a second sputtered material region thereon. In someembodiments, the method includes a step of adjusting a temperature ofthe substrate between the steps of sputtering the first sputteredmaterial region and forming the sensitized material region. The methodcan also include an optional step of sensitizing the first sputteredmaterial region using one of sputtering and PECVD to form a sensitizedmaterial region.

These and other features, aspects, and advantages of the presentapplication will become better understood with reference to thefollowing drawings, description, and claims.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

A more complete understanding of the present invention may be derived byreferring to the detailed description and claims when considered inconnection with the drawing figures, wherein like reference numbersrefer to similar elements throughout the drawing figures, and:

FIG. 1 is a simplified diagram of a deposition system in accordance withan exemplary embodiment;

FIG. 2 is a simplified sectional view of an iodine gas source inaccordance with an exemplary embodiment;

FIGS. 3 a and 3 b are simplified diagrams of a chamber in accordancewith an exemplary embodiment;

FIGS. 4 a and 4 b are simplified diagrams of another chamber inaccordance with an exemplary embodiment;

FIG. 5 is a simplified top view of a deposition chamber in accordancewith an exemplary embodiment;

FIGS. 6 a, 6 b, 6 c, and 6 d are simplified sectional views of lead saltmaterial regions formed with the chambers of FIGS. 1, 3 a and 3 b, and5;

FIG. 7 is a simplified flow chart of a method of depositing a lead saltmaterial region in accordance with an exemplary embodiment;

FIG. 8 illustrates a block diagram of an exemplary deposition system;

FIG. 9 illustrates a flow chart of an exemplary sputtering process;

FIG. 10 illustrates a flow chart of an exemplary sensitization process;and

FIG. 11 illustrates a flow chart of an exemplary passivation process.

DETAILED DESCRIPTION

While exemplary embodiments are described herein in sufficient detail toenable those skilled in the art to practice the invention, it should beunderstood that other embodiments may be realized and that logicalelectrical and mechanical changes may be made without departing from thespirit and scope of the invention. Thus, the following detaileddescription is presented for purposes of illustration only.

Turning now to the drawings, in which like reference characters indicatecorresponding elements throughout the several views, attention is firstdirected to FIG. 1 which shows a simplified diagram of a depositionsystem 10 in accordance with the present invention. Deposition system 10allows the deposition of separate material regions onto a substrate bysputtering and plasma enhanced chemical vapor deposition (PECVD) withoutundesirably exposing them to the outside atmosphere in betweendepositions.

Some of the material regions can include lead salt materials such aslead sulfide (PbS), lead selenide (PbSe), and lead telluride (PbTe).However, the material regions can also include semiconductor materialssuch as silicon (Si), silicon oxide (SiO), or silicon nitride (SiN),among others, It should be noted that a region can include one or morelayers of the same or different materials. Further, each layer caninclude an alloy of a material which includes two or more differentelements in various compositions. For example, a material region caninclude Pb_(0.55)S_(0.45), silicon oxynitride (SiON), or other alloysknown in the art.

In accordance with the invention, the lead salt or some of the othermaterial regions are deposited using sputtering. Sputtering is a termused to describe the mechanism in which atoms are dislodged from asurface of a target by collision with high-energy ions or particles. Thesputtering of the lead salt materials is typically done with RFsputtering in which the high-energy ions or particles are generated inresponse to a sputtering signal which varies with time. The sputteringsignal can also include a signal which is substantially constant withtime in addition to the time varying signal (i.e., bias sputtering). Insome embodiments, the sputtering can be done in the presence of amagnetic field (i.e., magnetron sputtering). These methods of sputteringand others are well known to those skilled in the art and will not beelaborated upon further here.

One reason the lead salt material regions are sputtered is so that theyadhere to the substrate better. This improves the reliability and yieldof any devices formed therewith. Another reason the lead salt materialregions are sputtered is because various reactants can be incorporatedin situ (i.e. reactive sputtering). For example, the reactants caninclude dopants which make the lead salt material region p-type orn-type when incorporated therein. The reactants can also include oxygen,which sensitizes the lead salt material region. The exposure of the leadsalt material region to oxygen can take place with or without thepresence of a halogen gas. Halogen gases typically include iodine,fluorine, bromide, and chlorine. When the lead salt material region issensitized, it is sensitive to incident IR radiation at highertemperatures, such as room temperature. The sensitization can becharacterized by measuring the resistivity of the lead salt material.The lead salt material regions can be sensitive to IR radiation at lowtemperatures, but it is generally desired to have the lead salt materialregion be sensitive to IR radiation at higher temperatures. This isbecause it is expensive and inconvenient to provide low temperatures.

In some embodiments, the sputtered lead salt material region is coatedwith a seal coating material region. This is typically done after thelead salt material region has been sensitized and before it is exposedto the outside atmosphere. The seal coating material region is chosen toprotect the lead salt material region from the outside atmosphere whenthe substrate is removed from deposition system 10. The outsideatmosphere can undesirably change the optical and/or electricalproperties of the lead salt material region.

Since sputtering and PECVD are used to form the various materialregions, these material regions have more consistent electrical and/oroptical properties from one deposition to another. This is becausedeposition system 10 allows the controllability of the amount and typeof elements the lead salt material region is exposed to before the sealcoating material region is deposited thereon. For example, the amount ofoxygen can he better controlled as well as its temperature because thedepositions occur in a controlled environment in a reaction chamber andnot in the outside atmosphere where undesired elements may be present.The seal coating material region stabilizes the electrical and/oroptical properties as a function of time because it is chosen to includea material which is impermeable by the outside atmosphere. In this way,undesired elements from the outside atmosphere are less likely to attachto the sensitized lead salt material region and undesirably alter itsproperties.

In this embodiment, deposition system 10 includes a vacuum reactionchamber 11 with a chamber space 12 defined by a housing 13 and a lid 14.Housing 13 is generally cylindrical in shape with sidewall 15, althoughit can have other shapes. A bottom parametric edge of sidewall 15 iscoupled to a bottom wall 16 and a top parametric edge is defined by anopening 17. A lip 18 extends outwardly around the periphery of the topparametric edge of side 1115 so that it receives lid 14.

Lid 14 encloses chamber space 12 when it is positioned on lip 18. Inthis way, lid 14 can be moved between an open position to allow accessto chamber space 12 and a closed position enclosing chamber space 12. Inthe closed position, lid 14 forms a seal with lip 18 so that a pressurein chamber space 12 can be controlled. The seal is facilitated by thepositioning of an O-ring 9 which extends around the periphery of lip 18.When lid 14 is in its closed position, a vacuum can be formed withinchamber space 12.

In accordance with the invention, an electrode 19 extends through lid 14and into chamber space 12. A target holder 20 is coupled to electrode 19so that it is held within space 12. A target 21 is carried by targetholder 20 so that it faces downwardly towards bottom wall 16. A coolingline 22 extends through lid 14 and into chamber space 12. Inside space12, cooling line 22 extends through target holder 20 and then back outof chamber space 12 through lid 14.

A substrate holder 23, which carries a substrate 24, is positioned inchamber space 12 near bottom wall 16 so that they both face upwardstowards target 21. In some examples and the others discussed herein,substrate holder 23 can rotate so that the materials deposited onsubstrate 24 are more uniform. Substrate 24 can include a semiconductormaterial, such as silicon, or another material onto which it is desiredto deposit a lead salt or other material regions. This is particularlyuseful because conventional deposition methods provide lead saltmaterial regions which adhere poorly to a silicon substrate. Goodadhesion of the lead salt material to the silicon substrate allows thefabrication of improved device structures with better yields. Thisprovides better device performance and reduces manufacturing costs. Forexample, in a photovoltaic device, the silicon substrate can have oneconductivity type and the sputtered lead salt material region can havean opposite conductivity type so that a p-n junction is formed, The leadsalt material region is sensitized so that this particular structure canbe used as an efficient and cost effective p-n junction for infraredapplications. One factor which determines its efficiency is the adhesionbetween the lead salt material region and the silicon substrate. This isbecause the interface between them is the p-n junction. As a result, ifthe adhesion is poor, then there will be more defects in the p-njunction which decreases its efficiency.

In an example of a photoconductive device, the silicon substrate canhave an insulating region positioned on its surface onto which the leadsalt material region is sputtered. The insulating region can includesilicon oxide, silicon nitride, or another insulator which reduces thecurrent flow between the lead salt material region and substrate. Thelead salt material region is sensitized and separate contacts are madeto the lead salt material region so the current flowing therebetween canbe sensed through the separate contacts. Since the current depends onradiation incident to the lead salt material region, this particularstructure can be used as an efficient and cost effective photodetector.

A heater 26 is positioned near substrate 24 to heat it up. Here, heater26 is positioned between substrate 24 and substrate holder 23, althoughin some examples, heater 26 can be otherwise positioned. For example, insome embodiments, heater 26 can be integrated with substrate holder 23.A cooling line 25 extends through bottom wall 16 and into chamber space12. Inside space 12, cooling line 25 extends through substrate holder 23and then back out of chamber space 12 through bottom wall 16.

Target holder 20 is thermally coupled to target 21 and substrate holder23 is thermally coupled to substrate 24 through heater 26 so thatcooling lines 22 and 25 can flow a coolant therethrough to adjust thetemperature of target 21 and substrate 24, respectively. The coolanttypically includes water, such as process chilled water, although it caninclude other coolants. Hence, cooling line 25 can be used to reduce thetemperature of substrate 24 to below room temperature and heater 26 canbe used to increase the temperature of substrate 24 to above roomtemperature.

It should be noted that the configuration of chamber 11 can be differentthan that shown in FIG. 1. For example, chamber 11 can be turned upsidedown so that material from target 21 is sputtered upwards instead ofdownwards. One advantage of this configuration is that it is less likelyfor substrate 24 to become contaminated. Also, chamber 11 could beshapes or any suitable configuration for performing one or more of thefunctions described herein.

In accordance with the invention, an electrode 27 is positioned withinreaction chamber 11. Electrode 27 is movable between a position betweentarget 21 and substrate 24 in an area 102 and a position away fromtarget 21 and substrate 24 in an area 103. In this particular example,when electrode 27 is in area 103 away from target 21 and substrate 24,it is positioned in an electrode chamber 28. Electrode chamber 28 iscoupled to sidewall 15 so that it opens up into chamber space 12. Inthis way, electrode 27 can be extended into or out of chamber space 12.

In FIG. 1, electrode 27 is shown in its retracted position where it isin area 103 in electrode chamber 28, It should be noted, however, thatelectrode 27 is generally movable between a position within chamberspace 12 where it can he used to deposit a material region ontosubstrate 24 using PECVD and a different position where it does notinterfere with the sputter deposition of material onto substrate 24.Accordingly, the particular movement of electrode 27 between areas 102and 103 shown in FIG. 1 is for illustrative purposes. Hence, in otherembodiments, electrode 27 can be moved to other positions where it doesnot interfere with the sputtering. For example, electrode 27 can bemoved between area 102 and a position near sidewall 15 when it isdesired to sputter.

In this embodiment, a vacuum system 30 is coupled to chamber 11 tocontrol the pressure of the atmosphere in chamber space 12 and to outgasthe gas and particles included therein, Vacuum system 30 includes avacuum hose 31 with an end coupled with chamber space 12 through bottomwall 16. An opposed end of vacuum hose 31 is coupled to ends of a vacuumhose 32 and a vacuum hose 33 to form a three-way intersection. Anopposed end of hose 32 is coupled to a mechanical pump 34 and an opposedend of vacuum hose 33 is coupled to a turbo pump 35. A pressure sensor36 is coupled to vacuum hose 32 and indicates the pressure of theatmosphere included therein. A shut off valve 37 and a throttle valve 38are also positioned within hose 32. Valves 37 and 38 can be opened toallow the atmosphere within chamber 11 to flow from chamber space 12through vacuum hoses 31 and 32, and through mechanical pump 34, where itis outgassed through an outlet 39 coupled to mechanical pump 34. Valves37 and 38 can also he closed to isolate mechanical pump 34 from vacuumhose 31.

A pressure sensor 40 is coupled to vacuum hose 33 and indicates thepressure of the atmosphere included therein. A shut off valve 41 and athrottle valve 42 are positioned within hose 33. Valves 42 and 43 can beopened to allow the atmosphere within chamber 11 to flow from chamberspace 12 through vacuum hoses 31 and 33, and through turbo pump 35,where it is outgassed through an outlet 43 coupled to turbo pump 35.Valves 41 and 42 can also be closed to isolate turbo pump 35 from vacuumhose 31.

When it is desired to have mechanical pump 34 communicate with chamberspace 12, valves 37 and 38 are open and valves 41 and 42 are closed sothat turbo pump 35 is isolated from vacuum hose 31. Mechanical pump 34is typically used to reduce the pressure of the atmosphere in chamberspace 12 from pressures around atmospheric pressure to lower pressures.To reduce the pressure of the atmosphere within chamber space 12 to evenlower pressures, turbo pump 35 is used. in this case, valves 37 and 38are closed and valves 41 and 42 are opened so that turbo pump 35 is incommunication with chamber space 12 through vacuum hose 31 andmechanical pump 34 is isolated from it. this embodiment, depositionsystem 10 includes an electrical system 50 to provide the variouselectrical signals for sputtering and PECVD. Electrical system 50includes an RE power supply 51 and a DC power supply 55. RE power supply51 typically provides time varying electrical signals, such asalternating current (AC) signals, and DC power supply 55 typicallyprovides electrical signals, which are substantially constant in time,such as direct current (DC) signals.

in this particular example, RE power supply Si provides an RE signalS_(RFA) and an RE signal S_(RFB) from outputs 60 and 61, respectively.Similarly, DC power supply 55 provides a DC signal S_(DCA) and a DCsignal S_(DCB) from outputs 58 and 59, respectively. Output 58 of DCpower supply 55 is coupled to heater 26 and output 59 of DC power supply55 is coupled to electrode 19. Signals S_(DCA) and S_(DCB) are providedto heater 26 and electrode 19, respectively, to provide a DC potentialdifference between them. The value of the DC potential difference can beused to control various properties of the sputtered lead salt materialregion. These properties can include the grain size, resistivity,surface roughness, impurity concentration, and alloy composition, amongothers.

Output 60 of RF power supply 51 is coupled to a current return 52 and aninput 62 to an RE transfer switch 54 through a variable capacitor 53.Output 61 of RE power supply 51 is coupled to an input 63 of RE transferswitch 54. RF transfer switch 54 has separate outputs 64, 65, and 66coupled to heater 26, electrode 27, and an input 67 of an impedancematching network 56, respectively. RE transfer switch 54 is configuredto provide desired signals from RF power supply 51 to heater 26,electrode 27, and impedance matching network 56 depending on the desiredoperation of reaction chamber 11, as will be discussed in more detailbelow. The particular signals outputted by RE transfer switch 54 can becontrolled in different ways. For example, a computer control system(not shown) can be coupled to switch 54 to control the signals outputtedat a particular time.

It should be noted that heater 26 is used as an electrode in thisembodiment for illustrative purposes. However, in other embodiments,substrate 24, substrate holder 23, or another conductive structure nearsubstrate 24 can operate as the electrode so that an electric field canbe provided between target 21 and substrate 24. In general, however,substrate 24, substrate holder 23, and heater 26 are electricallycoupled together so that they are at substantially the same potential.

Input 67 of impedance matching network 56 receives a signal from output66 of RF transfer switch 54 and conditions it to provide a signal with acertain amount of power at an output 68. This conditioned signal isprovided to electrode 19 through a capacitor 57 coupled therebetween. Inthis way, impedance matching network 56 is configured to conditionsignal S_(RFB) and provide a conditioned signal S_(RFC) so that adesired amount of power is transferred between RF power supply 51 andelectrode 19. Capacitor 57 is positioned between electrode 19 and output68 of network 56 so that the signal from output 59 of DC power supply 55does not flow into output 68 of network 56.

Deposition system 10 also includes a gas system 70 which providessputtering, process, and/or reactant gases to vacuum reaction chamber11. Gas system 70 includes a gas bottle 71 coupled to a gas line 73through a valve system 72. System 70 further includes an iodine gassource 110 coupled to a gas line 79 through a valve system 85. Gassystem 70 also includes gas bottles 74-78 coupled to gas line 79 throughrespective valve systems 80-84. When valve systems 80-84 are open, thegas in their corresponding gas bottles 74-78 can flow into gas line 79and when valve systems 80-84 are closed, then the gas in theircorresponding gas bottles 74-78 is blocked from flowing into gas line79. Valve systems 80-84 are also configured to prevent any gas in gasline 79 from undesirably flowing into corresponding gas bottles 74-78.In this way, valve systems 80-84 operate as one-way valves. Valve system72 operates as a one-way valve in a similar manner.

Gas bottle 71 typically includes a sputtering gas, such as argon (Ar),neon (Ne), or another gas typically used in sputter deposition. Gas line73 is coupled to chamber space 12 through sidewall 15 and positioned sothat the sputtering gas is flowed towards target 21 so that more of itis ionized during the sputter deposition. Gas bottles 74-78 typicallyinclude process gases. The process gases can include reactant gasestypically used in the deposition of material regions. These gases caninclude gases used for growth, such as silane, nitrous oxide, orammonia, among others. These gases can also include gases used fordoping, such as phosphine (PH₃) for n-doping or diborane (B₂H₆) forp-doping, and/or gases for sensitization, such as oxygen gas or halogengas. Other dopant gases include trimethylphosphite (IMP) andtrimethylborate (FMB). Gas line 79 is coupled to chamber space 12through sidewall 15 and positioned so that the process gases are flowedtowards substrate 24 so that more of it reacts with substrate 24 duringPECVD.

In this embodiment, deposition system 10 sputters the lead salt materialregion by using RF sputtering. For RF sputtering, RF power supply 51provides a time varying potential difference between electrode 19 andheater 26 by providing values for S_(RFA) and S_(RFB) to electrodes 19and 27 and heater 26 with RF power switch 54. Here, switch 54 outputssignal S_(RFB) to input 67 of impedance matching network 56 where it isconditioned to provide a signal S_(RFC), from output 68 to electrode 19.Switch 54 also outputs signal S_(RFA) at output 64 to heater 26, SignalS_(RFA) is made to be an RF ground by current return 52 so that there isa varying potential difference between electrode 19 and heater 26. Itshould be noted that signal S_(RFA) can be another reference potentialchosen so that electrode 19 operates as a cathode and heater 26 operatesas an anode. In sputter deposition with system 10, electrode 27 istypically provided with signal S_(RFA) so that its potential is definedby current return 52. However, the potential of electrode 27 can beother values which make it electrically inactive during the sputterdeposition.

When a sputtering gas is introduced into chamber space 12 through gasline 73, the sputtering gas is ionized by the potential differencebetween electrode 19 and heater 26 and the ions are directed towardstarget 21, When the ions collide with target 21, material from target 21is ejected towards substrate 24 where it forms a region of materialthereon. In this way, deposition system 10 provides sputter depositiononto substrate 24. It should be noted that the sputter deposition ontosubstrate 24 can take place directly on substrate 24 or it can takeplace on a material region previously deposited thereon. It should alsobe noted that in other embodiments, the sputtering of target 21 can bedone with an ion gun (not shown) which emits a stream of particles attarget 21. Hence, the use of sputtering gas ions in this embodiment isfor illustrative purposes.

The properties of a sputtered lead salt material region can becontrolled in several ways during the sputter deposition. For example,the adhesion of the sputtered lead salt material region can becontrolled by controlling the power output of RF power supply 51 and DCpower supply 55. The adhesion of the sputtered lead salt material regioncan also be controlled by controlling the pressure of the sputtering gaswithin chamber space 12. The pressure of the sputtering gas withinchamber space 12 can be controlled by controlling its flow rate throughgas line 73 by adjusting valve system 72.

The temperature of target 21 can also affect the properties of thesputtered lead salt material region. The temperature of target 21 can hecontrolled by adjusting the temperature and/or flow rate of the coolantflowing through cooling line 22. Likewise, the temperature of substrate24 can affect the properties of the sputtered lead salt material region,The temperature of substrate 24 can he controlled by controlling theflow rate and/or temperature of the coolant flowing through cooling line25 and the temperature output provided by heater 26. The temperature ofsubstrate 24 affects the properties of the sputtered lead salt materialregion since they are thermally coupled together. These properties caninclude the resistivity, grain size, composition, and stress, amongother properties.

In accordance with the invention, deposition system 10 also providesplasma enhanced chemical vapor deposition, in addition to sputterdeposition, to deposit a PECVD material region onto substrate 24. Itshould be noted that the deposition of the PECVD material region cantake place directly onto substrate 24 or it can take place on anothermaterial region previously deposited onto substrate 24. For example, thePECND material region can be deposited onto the sputtered lead saltmaterial region discussed above, The elements included in the PECVDmaterial region can be chosen to sensitize the sputtered lead saltmaterial region.

Conventional CND involves the formation of a non-volatile solid film ona substrate by the reaction of vapor phase gases (reactants) thatinclude the desired chemical constituents. The reactant gases areintroduced into a reaction chamber from a gas line and are decomposedand reacted at a heated surface of a substrate. However, in PECVD, aplasma is used to transfer energy to the reactant gases so that theydecompose in response to the plasma instead of the heated surface of thesubstrate. In this way, the deposition of the material region can bedone at much lower temperatures because the substrate does not have tobe heated up to cause the reaction.

One way PECVD is provided by deposition system 10 is in the followingmanner. The sputtering gas from gas line 73 is turned off and theprocess gases from gas line 79 is turned on so that the process gasesflows into chamber 11. Although the sputtering gas is turned off in thisexample, it can be left on in other examples to improve the uniformityof the PECVD material region. The process gases includes the reactantgases and its pressure is typically chosen so that the plasma moreeasily ionizes them. The plasma is generated by extending electrode 27out from chamber 28 so that it is positioned between target 21 andsubstrate 24 in area 102. A potential difference is provided betweenelectrode 27 and heater 26 so that the plasma is formed therebetween,Since it is desired in this example to use PECVD to deposit the materialregion onto substrate 24, signal S_(RFR) is provided to electrode 27 byoutput 65 of Rh power switch 54. Switch 54 also provides signal S_(RFA)from output 64 to heater 26 so that there is a potential differencebetween electrode 27 and heater 26 which provides the plasmatherebetween.

The plasma creates free electrons within the reactant gas. The electronscan gain sufficient energy from the electric field caused by thepotential difference so that when they collide with gas molecules in thereactant gas, gas-phase dissociation and ionization of the reactant gasoccurs. Some of the reactant gas is then adsorbed on substrate 24 or amaterial region previously deposited thereon. In this way, depositionsystem 10 provides both sputtering and PEND to deposit material regionson substrate 24.

Turn now to FIG. 6 a which shows an example of a structure 400 grownwith deposition chamber 10. In this example, structure 400 includessubstrate 24 onto which a lead region 402 is sputtered as describedabove. It should be noted that region 402 could include lead sulphur(PbS), lead telluride (PbTe), or other material regions, but leadselenide (PhSe) is shown here for illustrative purposes. Next, asensitized lead salt material region 403 is deposited thereon region 402by using either sputtering or PECVD.

If sputtering is used to deposit material region 403, oxygen gas isintroduced from gas line 79 into chamber 12, This can be done with orwithout the presence of a halogen gas, such as iodine. A dopant gas canalso be provided if it is desired to make material region 403 p-type orn-type. The oxygen can be provided by one of the gas bottles in system70 and the iodine gas can be provided by iodine gas source 110. Theargon from gas line 73 is ionized, as discussed above, and directedtowards target 21 where it causes material to be ejected therefrom. Theejected material from target 21 flows towards material region 402 onsubstrate 24 and interacts with the oxygen and iodine to form sensitizedmaterial region 403 thereon region 402.

The argon is injected near target 21 to reduce the amount of oxygen oriodine which would otherwise contaminate target 21. Similarly, theoxygen and iodine are injected near substrate 24 to increase thelikelihood of it being incorporated with region 403. The oxygen andiodine are also injected near substrate 24 so that any oxygen or iodinenot incorporated with region 403 is more likely to be outgassed throughvacuum system 30.

During the sputtering operation, signals S_(DCA) and S_(DCB) can beprovided by outputs 58 and 59 to heater 26 and electrode 19,respectively, to provide bias sputtering. In this way, the amount ofchemical constituents from the sputtering gas and dopant gasincorporated into material region 403 can be controlled.

If PECVD is used to deposit material region 403, then electrode 27 isused to form the plasma in chamber 12 between it and substrate 24 asdiscussed above. Argon or another sputtering gas can be flowed intochamber 12 through gas line 73 and oxygen is flowed into chamber 12through gas line 79. The sputtering gas can be flowed into chamber 12 toimprove the uniformity of region 403. The PECVD deposition of region 403can take place with or without iodine gas provided from iodine gassource 110. The temperature of substrate 24 is controlled with heater 26and/or cooling line 25 to provide it with a desired depositiontemperature. In this way, the deposition temperature can be adjusted toadjust the electrical and/or optical properties of material region 403.

in this embodiment, a seal coating material region 404 is then depositedon region 403 using PECVD, although it could he deposited usingsputtering in other embodiments. Material region 404 should include amaterial that is impermeable to the outside atmosphere. Examples of sealcoating materials include oxides, like silicon oxide (SiO), siliconnitride (SiN), and silicon oxynitride (SiON), among others. However, itcan also include other materials, such as aluminum nitride or amorphoussilicon. The particular choice of material for material region 404 willdepend on the gases included in gas system 70. For example, siliconoxide can be formed from oxygen and silane, silicon nitride can beformed from silane and ammonia gas, silicon oxynitride can be formedfrom silane, oxygen, and ammonia gas, and amorphous silicon can beformed from silane.

FIG. 2 is a simplified sectional view of iodine gas source 110 shown inFIG. 1. Gas source 110 includes a chamber 111 with a chamber space 112defined by a housing 113 and a lid 114. Housing 113 is generallycylindrical in shape with sidewall 115, although it can have othershapes. A bottom parametric edge of sidewall 115 is coupled to a bottomwall 116 and a top parametric edge is defined by an opening 117 which issurrounded by a lip 118. Lip 118 extends outwardly around the peripheryof the top parametric edge of sidewall 115 and receives lid 114. Lid 114is coupled to lip 118 near sidewall 115 so that it can engage lip 118when lid 114 encloses chamber space 112. In this way, lid 114 can bemoved between an open position to allow access to chamber space 112 anda closed position where it forms a seal with lip 117. The seal isfacilitated by the positioning of an O-ring 109 around the periphery oflip 117. Hence, lid 114 allows reciprocal movement between a retractedposition toward space 112 and an extended position away from space 112.When lid 114 is in its retracted position, a vacuum can be formed withinchamber space 112.

Gas source 110 includes a shelf 128 positioned in chamber space 112 forholding solid iodine 101. A heater 126 is positioned to heat solidiodine 101 so that a portion of it transforms into iodine gas 102. Inthis example, heater 126 is positioned outside housing 113 near sidewall115 and bottom wall 116, but it could be positioned elsewhere to provideheat to iodine 101. A temperature control system 127 is coupled to athermocouple 125. Thermocouple 125 extends through lid 114 and intochamber space 112 so that it can measure the temperature therein ofiodine gas 102. A pressure control system 129 also extends through lid114 and into chamber space 112 so that it can monitor the pressuretherein of iodine gas 102.

An end of a chamber gas outlet 119 extends through lid 114 so that it isin communication with chamber space 112 and an opposed end of chambergas outlet 119 is in communication with gas line 79. Valve system 85 iscoupled to chamber gas outlet 119 to control the flow of iodine gasbetween chamber space 112 and gas line 79. When valve system 85 is open,iodine gas 102 can flow into gas line 79 and when valve system 85 isiodine gas 102 is blocked from leaving chamber space 112. Valve system85 is also configured to prevent any gas in gas line 79 from undesirablyflowing into chamber space 112. In this way, valve system 85 operates asa one-way valve.

In this embodiment, temperature control system 127 and pressure controlsystem 129 are in communication with each other to provide a desiredtemperature and pressure to iodine gas 102 inside chamber 111. Hence, adesired amount of iodine gas 102 is formed from iodine 101. Inoperation, temperature control system 127 receives a temperature signalS_(Temp) from thermocouple 125 and a feedback signal S_(FB) frompressure control system 129. System 127 provides a heat signal S_(Heat)to heater 126 in response to signals S_(Temp) and S_(FB). Pressurecontrol system 129 receives a pressure signal S_(Pressure) from pressuresensor 130 and provides signal S_(pa) to temperature control system 127in response. Signals S_(Temp) and S_(Pressure) indicate the temperatureand pressure of iodine gas 102, respectively, in chamber space 112.

If the pressure of iodine gas 102 is too low as indicated by signalS_(pressure) then signal S_(FB) indicates this condition to system 127.As a result, system 127 outputs signal S_(Heat) to heater 126 so that itprovides more heat to increase the temperature of iodine gas 102. Inthis way, the temperature and, consequently, the pressure of iodine gas102 is increased to a desired value, Conversely, if the pressure ofiodine gas 102 is too high as indicated by signal S_(Pressure) thensignal S_(FB) indicates this condition to system 127. As a result,system 127 outputs signal S_(Heat) to heater 126 so that it providesless heat to decrease the temperature of iodine gas 102. In this way,the temperature and, consequently, the pressure of iodine gas 102 isdecreased to a desired value.

FIGS. 3 a and 3 b show simplified diagrams of a deposition system 150 inaccordance with the present invention. It should be noted that vacuumsystem 30 and gas system 70 are not shown in FIGS. 3 a and 3 b forsimplicity. In this embodiment, deposition system 150 includes twosputtering targets and two PECVD electrodes. System 150 similar to thatdescribed above in conjunction with FIG. 1.

System 150 further includes an electrode 99 which extends through lid 14and into chamber space 12. A target holder 90 is coupled to electrode 99so that it is carried in chamber space 12. In this example, electricalsystem 50 includes an RF power switch 96 with an input 45 coupled tooutput 68 of network 56 through capacitor 57. An output 47 of switch 96is coupled to electrode 19 and an output 46 of switch 96 is coupled toelectrode 99.

Target holder 90 carries a target 91 so that it faces downwardly towardsbottom wall 16. In this example, targets 21 and 91 are at non-zeroangles relative to substrate 24 although they could be parallel to it.Since targets 21 and 91 are at non-zero angles relative to substrate 24,it may be desired to rotate the substrate so that the material regionsdeposited thereon are more uniform. A cooling line 92 extends throughlid 14 and into chamber space 12. Inside space 12, cooling line 92extends through target holder 90 and then back out of chamber space 12through lid 14. Cooling line 92 can flow a coolant therethrough toadjust the temperature of target holder 90 and target 91 since holder 90and target 91 are thermally coupled together. The coolant typicallyincludes water, such as process chilled water, although it can includeother coolants.

In accordance with the invention, an electrode 98 is positioned withinreaction chamber 11. Electrode 98 is movable between a position 88 (FIG.3 b) between target 91 and substrate 24 in area 102 and a position 86(FIG. 3 a) away from target 91 and substrate 24. In this particularexample, when electrode 98 is in position 86 away from target 21 andsubstrate 24, it is positioned in an electrode chamber 97. Electrodechamber 97 is coupled to sidewall 15 so that it opens up into chamberspace 12, in this way, electrode 97 can be extended into or out ofchamber space 12. In this particular example, electrode chamber 98 ispositioned opposite electrode chamber 28, although it could be otherwisepositioned. Electrode 98 is coupled to an output 69 of RF power switch54 so that it can receive signals S_(RFA) and S_(RFB) from RIF powersupply 51 in a manner similar to electrode 27.

In accordance with the invention, targets 21 and 91 can include the sameor different materials. For example, targets 21 and 91 can include thesame or different lead salt materials. Hence, an advantage of depositionsystem 150 is that different lead salt material regions can be sputteredonto substrate 24. In another example, one of targets 21 and 91 caninclude a lead salt material and the other one can include a sealcoating material, such as silicon (Si) or aluminum (Al). An advantage ofthis is that a lead salt material region can be sputtered onto substrate24 and sensitized, then a seal coating material region can be sputteredthereon to protect the material regions between it and substrate 24 fromthe outside atmosphere. It should be noted that the seal coatingmaterial region can also be formed using PECVD as discussed above inconjunction with FIG. 1.

It should also be noted that deposition system 150 is shown as includingtwo targets (i.e. targets 21 and 91) for illustrative purposes, However,system 150 can include more than two targets so that more than twodifferent types of material regions can be deposited onto substrate 24.For example, system 150 can include three sputtering targets in whichtwo Of them include two different lead salt materials and the thirdtarget includes a material for seal coating, such as silicon to formsputtered amorphous silicon. In this way, two different sensitized leadsalt material regions can be sputtered onto substrate 24 and then theseal coating material region can be sputtered thereon.

The operation of deposition system 150 is similar to the operation ofdeposition system 10 discussed above. Briefly, FT power switch 54receives RF signals S_(RFA) and S_(RFB) at inputs 62 and 63,respectively, and provides these signals to electrodes 27 and 98, heater26, and impedance matching network 56. For example, if it is desired tosputter a material region onto substrate 24, then electrodes 27 and 98are moved to positions 87 and 86, respectively, and signal S_(RFA), isprovided to them so that they are at the reference potential defined bycurrent return 52. Signal S_(RFA) is also provided to heater 26 so thatits potential is defined by current return 52. Signal S_(RFR) isprovided to network 56 where it is conditioned as described above inconjunction with FIG. 1 to provide signal S_(RFC) to input 45 of RFpower switch 96.

If portions of target 21 are to he sputtered onto substrate 24, then RFpower switch 96 provides signal S_(RFC) to electrode 19 through output47 and electrode 99 is turned off by an appropriate signal at output 46.Hence, there is a potential difference between electrode 19 and heater26 so that target 21 is sputtered. Similarly, if portions of target 91are to be sputtered onto substrate 24, then RF power switch 96 providessignal S_(RFC) to electrode 99 at output 46 and electrode 19 is turnedoff by providing the appropriate signal at output 47. Hence, there is apotential difference between electrode 99 and heater 26 so that target91 is sputtered. It should be noted that electrodes 27 and 98 havepotentials defined by current return 52, but they could have otherpotentials during sputtering.

If it is desired to use PECVD to deposit a material region ontosubstrate 24, then at least one of electrodes 27 and 98 are moved topositions 89 and 88, respectively, and signal S_(RFB) is provided to atleast one of them. For example, if electrode 27 is to be used to provideplasma 101, then signal S_(RFA) is provided to electrode 98 from output69 of RF power switch 54 and signal S_(RFB) is provided to electrode 27from output 65. Signal S_(RFA) is provided to heater 26 from output 64so that there is a potential difference between heater 26 and electrode27 which provides plasma 101. Similarly, if electrode 98 is to be usedto provide plasma 101, then signal S_(RFA) is provided to electrode 27from output 65 and signal S_(RFB) is provided to electrode 98 fromoutput 69, in this way, there is a potential difference betweenelectrode 98 and heater 26 which provides plasma 101. Typically,electrodes 19 and 99 are provided with potentials so that they areelectrically inactive during PECVD.

Electrodes 27 and 98 can also be used to preclean targets 21 and 91,respectively. By precleaning targets 21 and 91 before sputtering amaterial region onto substrate 24, it is less likely that undesiredelements will be incorporated in the material region. This can be donewhen electrodes 27 and 98 are in corresponding positions 89 and 88.Target 21 can be precleaned by providing a potential difference betweenelectrodes 19 and 27 so that the sputter gas is ionized and impacts thesurface of target 21 to remove any impurities thereon. Similarly, target91 can be precleaned by providing a potential difference betweenelectrode 98 and 99 so that the sputter gas is ionized and impacts thesurface of target 91 to remove any impurities thereon.

Turn now to FIG. 6 b which shows an example of a structure 410 grownwith deposition chamber 150 of FIGS. 3 a and 3 b. Here, it isillustrated how system 150 can be used to deposit two different leadsalt material regions. In this example, structure 410 includes substrate24 onto which a lead selenide region 412 is sputtered using target 21.It should be noted that region 412 can include lead sulphur (PbS), leadtelluride (PbTe), or other material regions, but lead selenide (PbSe) isshown here for illustrative purposes. After region 412 is sputtered ontosubstrate 24, a sensitized material region 413 is positioned thereon byusing either sputtering or PECVD, as discussed above in conjunction withFIG. 6 a. After region 413 is formed, a lead sulfide material region 414is sputter deposited on it using target 91.

A sensitized material region 415 is then deposited thereon by usingeither sputtering or PECVD, as discussed above in conjunction with FIG.6 a. A seal coating material region 416 is deposited on sensitizedmaterial region 415 using PECVD, although it could be deposited bysputtering if a seal coating sputtering target is included thereinchamber 11. Since deposition system 150 can be used to deposit two ormore different lead salt material regions, it can be used to fabricatemore complicated structures which include multiple regions of differentlead salt materials. In general, the different lead salt materials aresensitive to different wavelengths of radiation which is useful forlight sensing applications.

FIGS. 4 a and 4 b show simplified diagrams of a deposition system 200 inaccordance with the present invention. It should be noted that vacuumsystem 30 and gas system 70 are not shown in FIGS. 4 a and 4 b forsimplicity. In this embodiment, deposition system 200 includes onesputtering target as in FIG. 1 and two electrodes as in FIGS. 3 a and 3b. Here, one electrode is used for PECVD and the other electrode is usedto preclean the sputtering target if desired.

Deposition system 200 includes electrode 19, target holder 20, andtarget 21, as described above in conjunction with FIG. 1. Electrode 98is positioned so that it is movable between position 88 between target21 and substrate 24 and position 8$ away from target 21 and substrate24. Likewise, electrode 27 is movable between position 89 between target21 and substrate 24 and position 87 away from target 21 and substrate24. Electrodes 27 and 98 move substantially parallel to target 21 andsubstrate 24.

Deposition system 200 can be used to provide sputter and PECVDdeposition in a manner similar to systems 10 and 150 discussed above. Inthe operation for sputtering, RF power supply 51 provides a potentialdifference between electrode 19 and substrate 24 by providing signalsS_(RFA) and S_(RFB) to electrodes 19, 27, and 98 and heater 26 with RFpower switch 54. Here, signal S_(RFB) is provided to impedance matchingnetwork 56 where it is conditioned to provide signal S_(RFC) toelectrode 19 through output 47 of RF power switch 96. Switch 54 providessignal S_(RFA) to heater 26 so that electrode 19 operates as a cathodeand heater 26 operates as an anode. The sputtering occurs in the sameway as described in conjunction with FIGS. 1, 3 a, and 3 b.

Deposition system 200 can also provide plasma enhanced chemical vapordeposition (CVD). This can be done in the following manner. Plasma 101is generated by extending electrode 98 out from chamber 97 so that it ispositioned between target 21 and substrate 24 in position 88 in area 102(FIG. 4 h). A potential difference is provided between electrode 98 andsubstrate 24 so that plasma 101 is formed therebetween. The potentialdifference is formed by providing signal S_(RFA) to heater 26 and signalS_(RFC) to electrode 98. Signal S_(RFC) is provided to electrode 98 byoutput 46 of RF power switch 96.

In this embodiment, electrode 27 can also be used to preclean target 21.This can be done when electrodes 27 is in position 89 (FIG. 4 b). Target21 can be cleaned by providing a potential difference between electrodes19 and 27 so that the sputter gas is ionized and impacts the surface oftarget 21 to remove any impurities thereon. In the operation forprecleaning target 21, RF power supply 51 provides a potentialdifference between electrode 19 and electrode 27 by providing signalsS_(RFB), and S_(RFA) to electrodes 19 and 27, respectively, through RFpower switch 54. Here, signal S_(RFB), is provided to impedance matchingnetwork 56 where it is conditioned to provide signal S_(RFC) toelectrode 19. Signal S_(RFC) is conditioned by network 56 so that adesired amount of power is provided to electrode 19 through output 47 ofRE power switch 96. Signal S_(RFA) is made to be RE ground by currentreturn 52 so that there is a potential difference between electrodes 19and 27.

FIG. 5 shows a simplified top view of a deposition system 300 inaccordance with the present invention. It should be noted thatdeposition system 300 can have many different configurations whichprovide substantially the same result and the particular configurationshown in FIG. 5 is for illustrative purposes. Deposition system 300includes a substrate transfer housing 302 with a plurality of openings(not shown). A substrate holder chamber 301 is coupled to an opening ofsubstrate transfer housing 302. Substrate holder chamber 301 isseparated from substrate transfer housing 302 by a door 321.

Substrate holder chamber 301 is used to store one or more substrates inwhich it is desired to form lead salt or other material regions thereon.Substrate transfer housing 302 is used to move the substrates from oneposition to another as will be discussed in more detail below. Themovement of the substrate can be done with the use of a mechanical arm,for example, or another structure known in the art.

In this particular embodiment, sputtering systems 303, 307, and 311 arecoupled to separate openings of substrate transfer housing 302.Sputtering systems 303, 307, and 311 are separated from substratetransfer housing 302 by doors 323, 328, and 331, respectively. Sputtersystems 303, 307, and 311 include sputter apparatus 304, 308, and 312,respectively. Sputter apparatus 304, 308, and 312 can include structuresimilar to the sputter apparatus shown in FIGS. 1, 3, and 4 as discussedabove.

Similarly, PECVD systems 305 and 309 are coupled to correspondingopenings of substrate transfer housing 302. PECVD systems 305 and 309are separated from substrate transfer housing 302 by corresponding doors325 and 329. PECVD systems 305 and 309 include PECVD apparatus 306 and310, respectively. PECVD apparatus 306 and 310 can include structuresimilar to the PECVD apparatus shown in FIGS. 1, 3, and 4 as discussedabove. Each door 321, 323, 325, 328, 329, and 331 are movable between afirst position away from substrate transfer housing 302 and a secondposition enclosing substrate transfer housing 302.

In operation, deposition system 300 has many of the advantages ofdeposition systems 10, 150, and 200 discussed above. For example,deposition system 300 provides both sputter and PECVD deposition. Hence,the substrates can be transferred between sputter systems 303, 307, and311 and PECVD systems 305 and 309 to deposit the various materialregions without undesirably exposing the substrate to the outsideatmosphere in between depositions. Further, sputtering systems 303, 307,and 311 can have sputtering targets of different lead salt materials sothat different lead salt material regions can be formed on thesubstrate.

Turn now to FIG. 6 c which shows a simplified sectional view of astructure 420 grown with deposition system 300 of FIG. 5. It should benoted that each sputter system can include one or more sputteringtargets. In this particular example, however, sputtering systems 303,307, and 311 include one sputtering target. Here, sputtering systems303, 307, and 311. Include a lead sulfide sputtering target, a leadtelluride sputtering target, and a lead selenide sputtering target,respectively.

In this example, structure 420 includes substrate 24 onto which a leadsulfide region 422 is sputtered using sputter apparatus 304. Afterregion 422 is sputtered onto substrate 24, a sensitized material region423 is deposited thereon by using either sputtering or PECVD, asdiscussed above in conjunction with FIG. 6 a, If sputtering is used toform region 423, then this can be done in sputtering apparatus 304. IfPECVD is used to form region 423, then this can be done using PECVDapparatus 306.

After region 423 is formed, substrate 24 is moved from either sputteringsystem 303 or PECVD system 305 to sputtering system 307. In sputteringsystem 307, a lead telluride material region 424 is sputtered ontomaterial region 423. A sensitized material region 425 is depositedthereon region 424 by using either sputtering or PECVD, as discussedabove in conjunction with FIG. 6 a. Again, if sputtering is used to formregion 425, then this can be done in sputtering apparatus 308. If PECVDis used to form region 425, then this can be done using PECVD apparatus310.

After region 425 is formed, substrate 24 is moved from either sputteringsystem 307 or PECVD system 309 to sputtering system 312. In sputteringsystem 312, a lead selenide material region 426 is sputtered ontomaterial region 425. A sensitized material region 427 is depositedthereon region 426 by using either sputtering or PECVD, as discussedabove in conjunction with FIG. 6 a. Again, if sputtering is used to formregion 427, then this can be done in sputtering apparatus 312. If PECVDis used to form region 427, then this can be done using PECVD apparatus310.

In this example, a seal coating material region 428 is then deposited onregion 427 using PECVD. Accordingly, material region 428 can bedeposited using any of the PECVD systems in system 300. However, sealcoating material region 428 can be deposited using sputtering. In thisway, deposition system 300 can be used to fabricate more complicatedstructures which include multiple regions of different lead saltmaterials. In general, the different lead salt materials are sensitiveto different wavelengths of radiation which is useful for light sensingapplications. It should be appreciated that the movement of substrate 24through system 300 depends on the desired layer structure and the layerstructure shown in FIG. 6 c is for illustrative purposes. The movementof substrate 24 through system 300 also depends on the desiredthroughput.

The throughput refers to the number of substrates that can be processedin a given amount of time, in system 300, more than one substrate can beprocessed simultaneously so that its throughput is increased. Forexample, while a lead salt material region is deposited on one substratein sputter system 303, another substrate with a lead salt materialregion already deposited on it can be sensitized with PECVD system 305.Of course, other substrates can be processed in sputtering system 307and PECVD systems 309 and 311 at the same time. The throughput can alsobe increased by depositing more than one material region in the samePECVD or sputtering system without moving substrate 24 through substratetransfer housing 302 between the two depositions. For example, a stackof a lead salt material region and insulating region can he deposited onsubstrate 24 using sputtering system 307.

Further, the movement of substrate 24 through system 300 is typicallychosen so that the transit time of the substrate is reduced. Forexample, the transit time of substrate 24 between sputtering system 303and PECVD system 305 is generally less than the transit time ofsubstrate 24 between sputtering system 303 and PECVD system 309.However, in some instances, PECVD system 309 may be the only PECVDsystem in system 300 that is currently not being used. In this case, itmay take less time to move the substrate to PECVD 309 rather than waitfor a closer PECVD system, such as PECVD system 305, to becomeavailable. Accordingly, it is typically desired to move substrate 24through system 300 so that more depositions can occur in a given amountof time. In this way, the throughput of system 300 is increased.

Turn now to FIG. 6 d which shows a simplified sectional view of astructure 440 grown with deposition system 300 of FIG. 5, FIG. 6 dillustrates that another advantage of system 300 is that both sides ofsubstrate 24 can be coated with lead salt materials. Here, a sensitizedlead salt material region is deposited on a surface 438 of substrate 24.This can be done as described above by using the various sputteringand/or PECVD systems included in deposition system 300. A seal coatingmaterial region 445 is then deposited thereon region 443 by using eithersputtering or PECVD. Substrate 24 can then be moved to another sputtersystem in system 300 through substrate transfer housing 302.

During the transfer of substrate 24, it can be turned over to expose anopposed surface 439. A lead salt sensitized material region 442 isdeposited on surface 439 of substrate 24. This can be done as describedabove by using the various sputtering and/or PECVD systems included indeposition system 300. A seal coating material region 444 is thendeposited thereon region 442 by using either sputtering or PECVD. Inthis way, substrate can be coated on both surfaces 438 and 439 which isuseful in some applications because there is more surface area to absorbmore incident radiation. In some applications, regions 443 and 442 caninclude different lead salt materials so that one spectrum of radiationis absorbed near surface 438 and another spectrum of radiation isabsorbed near surface 439.

FIG. 7 shows a method 500 of depositing a lead salt material region inaccordance with the present invention. It should be noted that method500 includes steps that can take place sequentially as discussed here orin a different order depending on the structure and properties of thedesired device to be formed. It should also be noted that some of thesteps are optional. At a start step 502, method 500 moves to a step 504of providing a deposition system with a reaction chamber and a step 506of positioning a substrate and a sputtering target into the reactionchamber. The deposition system is configured to deposit on thesubstrate. separate material regions using sputtering and/or PECVDwithout undesirably exposing the substrate to the outside atmospherebetween depositions.

The substrate can include a semiconductor material, such as silicon, oranother material onto which it is desired to deposit a material region.The substrate can also include structures positioned thereon, such assolar cells or other devices. The sputtering target can include leadsalt materials such as lead sulfide (PbS), lead selenide (PbSe), andlead telluride (PbTe). In some embodiments, more than one sputteringtarget of the same or different materials can be positioned in thereaction chamber. However, at least one target should be a lead saltsputtering target.

Method 500 includes a step 508 of providing a base pressure within thereaction chamber after it is sealed. The base pressure is chosen to atleast partially remove the atmosphere from within the reaction chamber.A step 510 includes providing a sputtering gas in the reaction chamber.The sputtering gas can include argon or nitrogen, for example, or othergases typically used in sputtering. A step 512 includes providing thesputtering gas within the reaction chamber with a pressure. This can bedone by controlling the flow rate of the sputtering gas into and out ofthe reaction chamber. The pressure is typically less than the pressureof the outside atmosphere, but it can be equal to or greater than theoutside atmosphere.

In an optional step 514, at least one of the sputtering targets isprecleaned to remove impurities or undesired elements from its surface.By precleaning the sputtering target, the likelihood of impurities orundesired elements being incorporated into the material region sputteredonto the substrate is reduced, From step 514, method 500 can move to astep 515 of providing a reactant gas into the reaction chamber. Thereactant gas can include a sensitizing gas, such as oxygen, to sensitizethe lead salt material region. The reactant gas can also include ahalogen gas and/or a dopant gas if desired. The dopant gas can providethe sputtered material region with an n-type or p-type conductivity. Inthis way, chemical constituents from the reactant gas can beincorporated into the sputtered lead salt material region in situ (i.e.reactive sputtering).

From step 515, method 500 includes a step 517 of sputtering a portion ofthe lead salt sputtering target onto the substrate or material regionspreviously deposited thereon to form a first lead salt material region.In one example, method 500 can then move to an optional step 520 ofdepositing a seal coating region onto the first lead salt materialregion. In another example, method 500 can repeat step 517 with the sameor different materials to provide a desired layer structure on thesubstrate. After the desired layer structure has been deposited, method500 can then move to step 520.

The seal coating material region protects the material regions betweenit and the substrate from the outside atmosphere so that undesiredelements are less likely to be incorporated therein. The seal coatingmaterial region can be deposited using sputtering or PECVD. Ifsputtering is used to deposit the seal coating material region, thensuitable coating target should be positioned in the deposition system instep 506 along with the other target(s). In one example, the suitablecoating target can include aluminum (Al), so that the seal coatingmaterial region can include aluminum nitride (AlN). If a silicon targetis used as the coating target, then the seal coating material region caninclude silicon oxide, silicon nitride, silicon oxy-nitride, oramorphous silicon, depending on which gases are flowed into the reactionchamber. If PECND is used to deposit the seal coating material region,then the appropriate gases are flowed into the reaction chamber.

In still another example, step 517 can more to a step 519 of performinga sensitization cycle. The sensitization cycle includes using PECVD tooxidize the uppermost portion of the first lead salt material region.After step 519, method 500 can move to optional step 520 of depositingthe seal coating material region. After step 519, method 500 can alsomove to step 517 or to step 515. In any of these examples, method 500moves from optional step 520 to a step 522 of removing the substratewith the material regions deposited thereon from the reaction chamber.This can be done by making the pressure within the reaction chambersubstantially equal to the pressure outside the reaction chamber so thatit can be opened up. Method 500 then ends with a step 524.

In another embodiment, method 500 can move from step 514 to a step 516of sputtering a portion of the lead salt sputtering target onto thesubstrate or material regions previously deposited thereon to form thefirst lead salt material region. Step 516 can be repeated with the sameor different materials to provide a desired layer structure on thesubstrate. From step 516, method 500 can move to step 520 directly orthrough a step 518 of performing a sensitization cycle. Here, step 518is similar to step 519 discussed above. From step 518, method 500 canthen move to optional step 520 of depositing the seal coating materialregion onto the first lead salt material region or the regionssubsequently deposited thereon. After step 520, as above, method 500moves to step 522 of removing the substrate, with the material regionsdeposited thereon, from the reaction chamber. Method 500 then ends withstep 524.

It should be noted that during either of steps 518 and 519, thetemperature of the substrate can be adjusted after steps 516 and 517,respectively. The temperature of the substrate at which the variousdepositions takes place affects the electrical and/or optical propertiesof the material regions deposited. Further, the sputtering in steps 515and 516 can be done in many different ways. For example, it can be doneusing RF sputtering with or without a DC bias (i.e. bias sputtering), itcan also be done using magnetron or reactive sputtering.

Method 500 is particularly useful for depositing a lead salt materialregion onto a silicon substrate, although it can be useful fordepositing the lead salt material region onto other substrates such asglass. Method 500 is also useful for sensitizing the lead salt materialregion. Depositing the lead salt material region onto silicon has been aproblem using conventional deposition methods because it may not adhereto the silicon substrate properly. If the lead salt material does notadhere properly, then the yield of devices will he low and the costswill be high. Another problem is that it is difficult to control thecomposition of the deposited lead salt material using conventionalmethods. As a result, the composition of the lead salt material regiontends to be different from one deposition to another. Further, usingconventional methods, the sensitization of the lead salt materialregions often leads to undesirable differences in resistivity from onelead salt material region to another.

In method, 500 these problems are at least partially solved for severalreasons. One reason is that the sputtered lead salt material regionproperly adheres to the silicon substrate. Further, the lead saltmaterial region can be conveniently sensitized during sputtering or byusing PECVD by introducing oxygen into the reaction chamber in acontrolled manner. The composition of the sputtered lead salt materialregion can be better controlled since it is sputtered in a reactionchamber where it is easy to control the atmosphere therein. As a result,the various chemical constituents that come into contact with the leadsalt material region can be better controlled. The chemical constituentscan undesirably become incorporated into the lead salt material regionto change its composition. The electrical and/or optical properties ofthe lead salt material depend on the composition, so if the compositionchanges then these will too. A further, advantage is that the sputteredlead salt material region can be conveniently seal coated so that itsresistivity is more stable as a function of time.

In accordance with an exemplary embodiment, adhering lead selenidematerials directly onto a substrate, without an intervening glass layeror thermal expansion buffer layer, facilitates using a sputteringprocess. In exemplary embodiments, the substrate comprises at least oneof silicon, gallium arsenide, or other suitable materials as would beknown to one skilled in the art. Moreover, the substrate material maycomprise various materials with coefficients of thermal expansiondifferent than lead selenide, material. Furthermore, the lead selenidefilm undergoes a sensitization process, resulting in a lead selenidefilm configured to respond to infrared radiation at room temperature.This is a beneficial improvement as typical lead selenide films requiresubstantial cooling to react to infrared radiation. In another exemplaryembodiment, a photovoltaic response to infrared radiation spectrum isconfigurable through using additional gases during processing or usingdopant materials. In yet another exemplary embodiment, lead selenidematerials adhered to a silicon substrate are configured to achievephotovoltaic operation as a p-n junction. additional junctions similarto a p-n junction are contemplated, such as a p-n-p junction comprisingmultiple lead selenide films.

As illustrated in FIG. 8, and as briefly described above with regards tomethod 500, an exemplary process of adhering lead selenide materials ona substrate comprises sputtering the lead selenide directly onto thesubstrate, sensitizing the lead selenide film, and sealing the leadselenide film in a passivation system. More specifically, in anexemplary process a silicon substrate is placed in a sputtering system,where the sputtering system comprises a means to heat the substrate anda target assembly with the appropriate lead selenide material to bedeposited on the substrate. The deposition process is performed untilthe desired thickness of lead selenide material is deposited on thesubstrate. Moreover, in an exemplary embodiment, the lead selenidematerials are directly adhered to the substrate without a glass layer inbetween. In the prior art, a glass layer was placed between a materialand lead selenide film to act as a buffer and compensate for differentcoefficients of thermal expansion of the lead selenide film and othermaterial. Using a glass buffer layer in a photoconductive applicationincreases the cost, manufacturing time, and difficulty to interface thelead selenide film with other electronic components. In a photovoltaicapplication, a glass buffer layer cannot be present in order for theapplication to operate. However, by using the exemplary depositionprocess, the substrate and the lead selenide materials form a p-njunction with no glass layer or thermal expansion buffer in between.

After depositing the lead selenide, the substrate is removed from thesputtering system but remains in a controlled environment, or exposed toair for a short period of time, while transferred to a sensitizationsystem. In the sensitization system, gaseous contaminants are removedfrom a process chamber using a vacuum assembly and the process chamberis filled with an inert gas until reaching a desired pressure. In anexemplary embodiment, the process chamber is at least one of an etchingchamber, a deposition chamber, or a thermal processing chamber, in oneembodiment, the inert gas is nitrogen and the desired pressure is in therange of atmospheric pressure to 3 pounds per square inch (PSIG). Inanother embodiment, the desired pressure is in the range of 0 to 10PSIG. In yet another embodiment, the desired pressure may be anysuitable pressure for the sensitization process.

In the exemplary process, gaseous iodine, nitrogen, and oxygen areintroduced into the process chamber, with the process chamber at anelevated temperature. For example, the process chamber may be at atemperature in the range of 0 to 400° C., or more specifically heated to300° C. Furthermore, the ratio of gases and time of exposure can beconfigured to adjust the sensitization process and response to infraredradiation.

After the sensitization process, the substrate is transferred to apassivation system through a controlled environment. The passivationsystem may also be referred to as a plasma deposition system. A passivelayer configured to provide a passive layer of protection fromcontaminants is deposited on the substrate. In one embodiment, thepassive layer is silicon nitride or oxy-nitride.

The specific process parameters and numbers disclosed herein are forillustration purposes only. The actual process parameters to enable thedisclosed process are variable and dependent on process conditions.Thus, a range of values and settings are contemplated beyond thespecific values and specifics recited herein. The process conditionsinclude, but are not limited to, the number of substrates beingprocessed at a time, the size of the substrates, the size of theprocessing chamber(s), the substrate material(s), DC biasing, or anycombination of these conditions. Furthermore, the process values andsettings are also dependent on the desired outcome, such asmanufacturing a substrate with acceptable film characteristics.Moreover, considerations also include the manufacturing process itself.For example, reducing the process time for manufacturing a substrate.

The process described herein is an exemplary embodiment of manufacturinga substrate of about ¼ inch to 2 inches. Furthermore, the substrate isprocessed in a deposition chamber that is about 18 inches in diameterwith a height of about 8 inches. In this exemplary embodiment, thesensitization chamber is about 5 inches in diameter and about 7 incheslong.

In an exemplary embodiment and with reference to FIG. 8, a sputteringsystem 840 comprises a sputtering process controller 820, a gas panelsection 830 with gas flow control devices, a heater substrate holder841, a trap 843 configured to collect excess lead selenide materialsbefore the materials reach a vacuum pump assembly 850, and an RFgenerator and matching network 844.

Moreover, in an exemplary embodiment, a process for depositing leadselenide materials uses sputtering. Initially, a substrate is placedinto a sputtering system along with a sputtering target. In an exemplaryembodiment, the sputtering target is the lead selenide material. Duringthe sputtering process, an injected gas molecule slams into thesputtering target, and the collision breaks off a piece of the leadselenide, which transfers to the substrate. The piece of lead selenidetravels at a high velocity when striking the substrate, generating animpact that results in the lead selenide adhering to the substratematerial (e.g., a silicon substrate). In an exemplary embodiment, thedeposited lead selenide does not lift or peel off when additionalprocessing is performed on the film after deposition at elevatedtemperatures.

In accordance with an exemplary embodiment, process parameters may beconfigured to adjust the film's electrical properties. The processparameters include, but are not limited to, temperature, pressure, gasflow rates, and deposition rates. For example, increasing thetemperature of the substrate facilitates control of the grain size ofthe lead selenide material being deposited, and thus affects variouselectrical properties of the film, In another exemplary embodiment,dopants are incorporated in the sputtering process to adjust the film'sinfrared radiation response at different wavelengths.

In an exemplary embodiment, and for purposes of illustration, theprocessing conditions may include the following characteristics. Thesteps of FIG. 9 may be taken sequentially, though the process is notlimited as such. Moreover, various steps are optional. First, asubstrate is placed on an anode (Step 905), where the anode may haveheating capabilities. The chamber walls are heated to about 150° C. toreduce contaminants (e.g., moisture) present on the interior walls (Step910) of the process chamber and the system is pumped down to evacuateremaining contaminants (Step 91). Furthermore, the system is purged ofcontaminants using Argon, for example at a pressure of 1 Torr for abouttwo minutes (Step 920). in other embodiments, the system is purged withan inert gas, such as helium, hydrogen, nitrogen, or other suitablegases. While the substrate is surrounded by Argon, the temperature iselevated up to 320° C. for about 5 minutes (Step 925). At this time, thepressure of the system is set to 60 mille Torr with 300 seem of argonflowing in the process chamber (Step 930). Additionally, the anode andcathode are placed about 3 inches apart, and an RF power source isturned on at 50 watts for about 5 minutes (Step 935). Then, the RF powersource is increased to 100 watts within 1 minute and remains at 100watts for a period of 50 minutes (Step 940). Furthermore, the RF powersource is turned off, the temperature is reduced to 100° C. and theprocess chamber is filled with nitrogen until atmospheric pressure isreached (Step 945). In the exemplary embodiment, this process results ina 1 micron thick film of lead selenide on the silicon substrate.

Once a lead selenide coating is deposited on the substrate, exposure toair may alter the electrical properties. In an exemplary embodiment, thesubstrate is transferred to a controlled environment with no air toprevent changes in the film due to exposure to air, allowing forrepeatable film properties.

In accordance with an exemplary embodiment and with momentary referenceto FIG. 8, a sensitization system 890 comprises a sensitization processcontroller 860, a controlled environment 870 for the transfer of thesubstrate from the sputtering system to the sensitization system, a gaspanel section 880 with gas flow control devices, a heated substrateholder 891 to facilitate increasing the substrate temperature to 300° C.to 400° C. a first iodine trap 8100 and a second iodine trap 8130individually configured to prevent transfer of iodine gas into theatmosphere, a vacuum pump assembly 8110 configured to operate fromvacuum to atmospheric conditions, and an iodine delivery system 8120.

In an exemplary method, a sensitization process comprises transferringthe substrate into a sensitization system to perform sensitization ofthe lead selenide material, The temperature range of the sensitizationprocess may he from ambient temperature up to 400° C. In the exemplarymethod, lead selenide material is exposed to a combination of nitrogen,oxygen, or another halogen gas, resulting in a reaction that alters thelead selenide material's electrical and infrared radiation response, andthus configuring the lead selenide material to respond to infraredradiation at room temperature. A photoconductive response is when thelead selenide material becomes more conductive if infrared radiation isabsorbed. A response is the production of a voltage difference in thelead selenide material if infrared radiation is absorbed. The halogengas is one of fluorine, chlorine, bromine, iodine, and astatine. In anexemplary embodiment, the halogen gas most suited for efficientperformance may vary between specific applications. For purposes ofillustration only, iodine gas is used as the preferred halogen gas.

Furthermore, in another exemplary embodiment, the sensitization processfacilitates an infrared radiation response that is 5 or 6 times betterthan typical sensitization processes. in other words, a typicalphotoconductive application using a lead selenide film has a resistancechange (i.e., photoconductive response) in the 5-7% range if exposed toinfrared radiation. An exemplary photoconductive application using alead selenide film has a photoconductive response in the range of20-30%. in another exemplary embodiment, the photoconductive applicationusing a lead selenide film as described herein may have aphotoconductive response greater than 7%. In yet another embodiment, thephotoconductive response may be greater than 10%. In yet still anotherexemplary embodiment, the photoconductive response may be greater than20%. Moreover, an exemplary photovoltaic application using a leadselenide film is configured to generate a voltage in response toinfrared radiation exposure.

For illustration purposes, an exemplary sensitization process isdescribed with reference to FIG. 10. After a substrate has a leadselenide film deposited, the substrate begins the sensitization processwith little or no exposure to air and held at a temperature of about100° C. (Step 1005). For example, the substrate is either transferredfrom a controlled environment or exposed to air for less thanapproximately 30 seconds before being heated. Next, the process chamberis closed and all, or substantially all, air or air associatedcontaminants are removed using a vacuum system (Step 1010). Once thevacuum has removed the contaminants, the process chamber is backfilledwith nitrogen until atmospheric pressure is reached, and a nitrogenpurge (500 seem) is run for about five minutes (Step 1015). Inaccordance with the exemplary sensitization process, the substrate isheated at 300′ C. for about four minutes in the 500 SCCM of nitrogen(Step 1020).

In an exemplary process, an area behind a restrictor is pumped on by avacuum system for about one minute (Step 1025). Also in the exemplaryprocess, the iodine source has a temperature of approximately 183° C.and is maintained in the gaseous state at a pressure of about 2 PSIG(Step 1030). Furthermore, the iodine gas flows through the resistor at arate of 0.032 seem for a period of about one minute to establish aconsistent flow (Step 1035). The excess iodine as is exhausted through acool trap to the atmosphere (Step 1040). After the iodine flow isestablished, a heated valve opens, allowing the iodine gas to enter theprocess chamber where the substrate is located, with the process chamberhaving a pressure of about 760 Torr (Step 1045). Once iodine is flowingfor about 30 seconds, oxygen enters the process chamber at a flow rateof 0.5 seem per minute (Step 1050). An iodine oxygen mixture flowsthrough the process chamber (Step 1055) for about 2 minutes, after whichthe iodine and oxygen flows are turned off. Then the nitrogen flowincreases to 3 liters per minute and the process chamber temperaturecools off to about 100° C. (Step 1060).

In accordance with an exemplary embodiment and with momentary referenceto FIG. 8, a passivation system 8160 comprises a passivation processcontroller 8150, a controlled environment 8140 for the transfer of thesubstrate from the sensitization system to the passivation system, an RFgenerator and matching network 8162, a vacuum pump assembly 8170, and agas panel section 8180 with gas flow control devices.

After the sensitization process, the substrate is placed in controlledenvironment 8140 because the electrical properties of the film may beaffected by exposure to air. In an exemplary embodiment, the film'selectrical properties are protected by passivation material deposited onthe film via a plasma deposition system. In various embodiments, thepassivation material may be a plasma deposited silicon nitride oroxy-nitride film. An advantage of using the oxy-nitride film is theoxy-nitride film can be configured to adjust the refractive index andprovide less interference with the infrared response of the leadselenide material.

The passivation of semiconductor devices using various steps is wellknown. However, for illustration purposes, an exemplary nitridepassivation process is described with reference to FIG. 11. Initially, asubstrate with lead selenide sensitized deposited material is placed ina plasma deposition system (Step 1105), In an exemplary process, thesubstrate enters the deposition system directly from controlledenvironment 8140, or is exposed to air for less than 30 seconds. Thesubstrate is placed on a heater assembly at a temperature of about 100°C. Furthermore, the pressure inside the process chamber is reduced tothe base pressure of a vacuum pump (Step 1110). In one embodiment, thebase pressure of vacuum pump is the lowest pressure level that vacuumpump is capable of achieving in the process chamber. Next, a nitrogenpurge flow is established at 500 seem (Step 1115) and the processchamber's pressure is increased to 2 Torr. Furthermore, the temperatureis increased to about 380° C. within 3 minutes of heating (Step 1120).In the exemplary process, silane is added at a rate of 10 seem andammonia is added at a rate of 80 seem (Step 1125). At this point, theprocess chamber environment is held steady at about 380° C. and 2 Torr(Step 1130). The next step is turning on an RF power source to provide80 watts for about 15 minutes (Step 1135). In an exemplary embodiment,this process results in an 8000 angstrom thick passivation filmdeposited on top of the lead selenide film. After the passivation filmis deposited, the process chamber pressure is reduced to the vacuum pumpbase pressure (Step 1140) and then purged with 500 seem of nitrogenwhile the substrate cools down to less than 100° C. in an exemplaryprocess, the process chamber is then backfilled with nitrogen toincrease the process chamber pressure (Step 1145) before removing thesubstrate to complete the nitride passivation process.

Thus, in an exemplary embodiment, a substrate undergoes a depositionprocess where a lead selenide material is directly adhered to thesubstrate without an intervening glass layer, Furthermore, the substrateundergoes a sensitization process that facilitates the lead selenidematerial reacting to infrared radiation at ambient temperature. Then, apassivation process is performed upon the substrate to prevent the leadselenide materials from reacting to environmental contaminants thatcould degrade the operation and performance of the overall substrate.

Although described herein as moving a substrate between processes insome embodiments, albeit in a controlled environment, it should berecognized that a single process chamber could be used for all thedescribed processes. Stated another way, a single process chamber couldbe used for the deposition process, the sensitization process, thepassivation process, or any combination thereof. Thus, the substratecould remain in a process chamber without the need to be transferred ina controlled environment.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as critical, required, or essentialfeatures or elements of any or all the claims. As used herein, the terms“includes,” “including,” “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises a list ofelements does not include only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, no element described herein is requiredfor the practice of the invention unless expressly described as“essential” or “critical.”

1. A substrate comprising: a lead selenide film directly adhered to thesubstrate, wherein the material of the substrate has a coefficient ofthermal expansion different than lead selenide material; wherein thesubstrate is configured to respond to infrared radiation at ambienttemperature.
 2. The substrate of claim 1, wherein the substrate is asilicon substrate,
 3. The substrate of claim 1, absent a glass layerbetween the lead selenide film and the substrate.
 4. The substrate ofclaim 3, wherein the lead selenide film is configured for at least oneof photoconductive and photovoltaic applications.
 5. The substrate ofclaim 1, further comprising a passivation film on the lead selenidefilm, wherein the passivation film is configured to substantiallyeliminate alteration of electrical properties of the substrate inresponse to exposure to contaminants.
 6. The substrate of claim 1,wherein the substrate is a silicon substrate or a gallium arsenidesubstrate.
 7. The substrate of claim 1, wherein the substrate isconfigured to respond to infrared radiation at ambient temperature bysensitizing the substrate, and wherein the sensitizing the substratecomprises: removing contaminants from a process chamber; the processchamber with an inert gas; and adding a combination of halogen, gas,nitrogen gas, and oxygen gas to the process chamber, wherein the processchamber is heated to about 300° C.
 8. The substrate of claim 1, whereinthe halogen gas is at least one of fluorine, chlorine, bromine, iodine,and astatine.
 9. The substrate of claim 1, wherein the inert gas isnitrogen gas, and wherein the pressure of the process chamber is in therange of atmospheric pressure to 3 pounds per square inch.
 10. Thesubstrate of claim 1, wherein the lead selenide film is configured for aphotoconductive response greater than 10%.
 11. A method for creating ap-n junction on a substrate, said method comprising: sputtering a leadselenide film on the substrate, wherein the material of the substratehas a coefficient of thermal expansion different than lead selenidematerial; heating the substrate in the range of 300°-400° C.; andconfiguring a photovoltaic response of the lead selenide film toinfrared radiation at ambient temperature.
 12. The method of claim 11,wherein the substrate is a silicon substrate.
 13. The method of claim11, wherein the substrate is a gallium arsenide substrate.
 14. Themethod of claim 11, wherein the configuring the photovoltaic responsecomprises adding dopant materials to a sputtering target used in thesputtering the lead selenide film.
 15. The method of claim 11, whereinthe configuring the photovoltaic response comprises adding a gas to asputtering target used in the sputtering the lead selenide film.
 16. Themethod of claim 11, wherein the configuring the photovoltaic responsecomprises sensitizing the substrate, and wherein the sensitizing thesubstrate comprises: removing contaminants from a process chamber;filling the process chamber with an inert gas; and adding a combinationof halogen gas, nitrogen gas, and oxygen gas to the process chamber,wherein the process chamber is heated to about 300° C.
 17. The method ofclaim 16, wherein the inert gas is nitrogen gas, and wherein thepressure of the process chamber is in the range of atmospheric pressureto 3 pounds per square inch.
 18. The method of claim 16, furthercomprising: adjusting a gas ratio of the combination of halogen gas,nitrogen gas, and oxygen gas; and configuring electrical properties ofthe substrate via adjusting a time of exposure of the substrate to thecombination of halogen gas, nitrogen gas, and oxygen gas.
 19. The methodof claim 16, wherein the halogen gas is at least one of fluorine,chlorine, bromine, iodine, and astatine.
 20. The method of claim 11,wherein the lead selenide film is configured for a photoconductiveresponse greater than 7%.